The present invention relates to test and measurement instruments, and more particularly to an automatic anomalous event detection method for a digital oscilloscope that automatically detects when anomalous events are occurring and captures such an anomalous event.
In a digital oscilloscope an input analog signal is input both to a digitizer for conversion into digital data for storage in a waveform memory and to a trigger circuit where a trigger signal is derived either from the input analog signal itself or from an external signal, as is well known in the art. The generation of the trigger signal causes the digital oscilloscope to "freeze" a portion of the input analog signal in the waveform memory, the portion being a function of the trigger signal as determined by an operator--pre-trigger, post-trigger or a combination thereof. The trigger signal is generated periodically at the first occurrence of a triggering event, usually the crossing of a threshold level, after a hold-off period from a prior trigger signal determined by the oscilloscope setup.
More recently digital oscilloscopes provide advanced trigger circuitry that allows the generation of trigger signals upon anomalous events. Such advanced trigger circuitry allows the detection of time qualified signals, i.e., signals having pulse widths less than a reference time interval (glitches), greater than the reference time interval, or within or without the reference time interval. The circuitry also allows the detection of voltage qualified signals using dual thresholds, i.e., when a signal crosses and recrosses one threshold while not crossing the other threshold (runts), or is in a metastable state between the two thresholds.
The uninitiated users are likely to find that these functions of the advanced trigger circuitry are not easy to use or are not readily accessible. The anomalous events that the advanced trigger circuitry is designed to detect are embedded in the analog input signal and occur at infrequent rates much lower than the analog input signal's average repetition rate.
What is desired is an automatic anomalous event detection method that brings the functionality of such advanced trigger circuitry to the level of the uninitiated users.